Color display system



Dec. 17, 1968 w. T. MATZEN 3,4 6,731

COLOR DISPLAY SYSTEM Filed April 30, v1965 2 Sheets-Sheet 1 FROMDETECTION FIG CIRCUITS AMP FR D F GA RA OM E LECTION CI ITS FROMAUXILIARY DEF'LECTION CIRCUITS Hv Y (-I LOW VOLTAGE HIGH VOLTAGE.

SU PPLY SUPPLY Dec. 17, 1968 w.'r. MATZEN 3,416,731

conon DISPLAY SYSTEM Filed April 50, 1965 2 Sheets-Sheet 2 FROMDETECTION FIGZ.

CIRCUITS G-Y AMP FROM DEFLECTION CIRCUITS GA RA LOW VOLTAGE W SUPPLY (-1HIGH VOLTAG E SUPPLY REFERENCE VO LTAG E 7 HM REFERENCE H.V.

VOLTAGE United States Patent 3,416,731 COLOR DISPLAY SYSTEM Walter T.Matzen, Richardson, Tex., assignor to Texas Instruments Incorporated,Dallas, Tex., a corporation of Delaware Filed Apr. 30, 1965, Ser. No.452,301 8 Claims. (Cl. 315-13) ABSTRACT OF THE DISCLOSURE Thisspecification discloses a combination, employed in a color displaysystem, characterized by a viewing screen having phosphors which emitlight of different colors when energized by electron beams of differentenergies; electron beam guns and deflection coils for scanning thescreen with beams of electrons under different accelerating voltagesand, hence, different velocities; high voltage supply in combinationwith the electron beam guns for providing a first and a secondaccelerating voltage; and regulator circuit for regulating the voltagedifferential between the first accelerating voltage and the secondaccelerating voltage in accord with the differential deflection forceapplied to the first beam of electrons and to the second beam ofelectrons and in response to feedback from the high voltage portion ofthe first accelerating voltage, such as may be applied to the screen. Inthis way registration is maintained between the image componentsprovided by the beams of electrons on the screen despite variations inthe absolute value of the accelerating voltages,

This invention relates to a color display system and more particularlyto an improved color display system employing an electron beam atdifferent electron energies to differently energize various phosphors toemit light of various hues.

Various polychromatic color display systems have been proposed in whichthe different color phosphors are differently responsive to electronbeams of different energies or velocities so that various hues of lightcan be produced by varying the beam electron accelerating voltage.However, the use of more than one accelerating voltage requires that thesystem include some form of deflection compensation to correct forvariations in deflection caused by the varying velocities of differentelectrons. If uncorrected, these variations in deflection causemisregistration between the different component monochromatic imageswhich constitute the polychromatic display. Since the amount ofcorrection necessary depends upon the particular accelerating voltageapplied, typical color displays have heretofore employed relativelycomplicated and expensive systems for regulating the high potentialaccelerating voltages.

Among the several objects of the invention may be noted the provision ofa composite multicolor display system having improved registrationbetween component monochromatic images; the provision of such a systemwhich avoids the necessity of regulating high electron beam acceleratingvoltages; the provision of such a system in which variations due to thecontamination of exposed high voltage circuits are minimized; theprovision of a multigun kinescope system in which the voltagedifferential between guns is precisely regulated; and the provision ofsuch a system which is relatively simple in construction and is reliablein operation. Other objects and features will be in part apparent and inpart pointed out hereinafter.

Briefly, the invention involves a color display system having a viewingscreen including phosphors which emit light of different colors whenenergized by electron beams Patented Dec. 17, 1968 Ice of differentenergies. An electron beam gun is provided for scanning the screen witha beam of electrons and at least two electron beam accelerating voltagesare provided for energizing said phosphors to emit light of differentcolors. The system also includes means for regulating the voltagedifferential between the two accelerating voltages as a function of thetotal value of one of these accelerating voltages for maintainingregistration between the image components provided by electronsaccelerated by the two different voltages even though their absolutevalues fluctuate due to any of a variety of causes.

The invention accordingly comprises the apparatus and methodshereinafter described, the scope of the invention being indicated in thefollowing claims.

In the accompanying drawings in which several of various possibleembodiments of the invention are illustrated,

FIGURE 1 illustrates, in diagrammatic form, a color display systemincluding a two-gun kinescope in which a negative voltage differentialis applied between the guns;

FIGURE 2 illustrates another embodiment in which a positive voltagedifferential is applied between the two guns of a kinescope;

FIGURE 3 illustrates a kinescope including a resistive voltage dividersealed within the kinescope envelope; and

FIGURE 4 shows a modification of the kinescope of FIGURE 3 in which thedivider is in the form of a deposited resistive film.

Corresponding reference characters indicate corre sponding partsthroughout the several views of the drawmgs.

Referring now to FIGURE 1, the color display system illustrated thereincludes a kinescope 11 for two-color presentation of polychromaticimages. The two colors which can be produced by the tube are red andwhite. The kinescope 11 comprises a viewing screen 13 including a glassface plate 15 through which the image is viewed. Coated on the insidesurface of plate 15 is a phosphor layer 17 which when energized emitslight through the face plate 15. Layer 17 is constituted by a mixture ofphosphor particles 19 and 21. Particles 19 emit substantially red lightwhen energized while the particles 21 emit substantially cyan light whenenergized. Layer 17 of phosphor particles is in turn coated with a thindeposited aluminum film 23 by means of which an electron beamaccelerating voltage is applied to the screen 13 from a high voltagepower supply HV.

The particles 19 and 21 respond differently to electron beams of varyingenergy. The particles 19 are energized when struck by electrons whichhave been accelerated by a relatively low voltage so as to possess arelatively low electron energy While the cyan particles 21 emit lightonly when struck by electrons which have been accelerated by arelatively high voltage. The difference in sensitivity of the phosphorsto electron beams of different energies is produced by providing abarrier layer on the cyanemitting particles. The barrier produces araised voltage or electron energy threshold which must be exceededbefore the particle is energized to emit light. Alternatively, bothparticles 19 and 20 are provided with barriers with the cyan particlesbeing given a thicker barrier to achieve the desired differentialbetween the threshold of the two different kinds of particles. Asuitable barrier layer is a coating of silicon dioxide deposited onindividual particles. This coating is deposited, for example, by thecracking of a tetraethoxysilane atmosphere within which the phosphorparticles are suspended.

It can be seen that an electron beam accelerated by a voltage which isintermediate the energization threshold voltages of the particles 19 and21 will excite only the red phosphor particles 19 whereas an electronbeam accelerated by a voltage greater than both of these thresholds willenergize both the red and the cyan phosphors. Since cyan iscomplementary in color to red, the high energy electrons will thus causea substantially white or achromatic light to be emitted. It shouldfurther be understood that various mixtures of white and red light canbe obtained by producing an electron beam containing electrons of bothenergies. The composite beam can be formed either by the mixture of twobeams, both opera tive simultaneously, or by providing a single beam ofalternating energy levels.

Kinescope 11 also includes a neck portion 25 within which are supportedtwo essentially conventional electron beam guns 27 and 29. Each gun 27and 29 includes a cathode, 31 and 33 respectively, which emits electronswhen heated by a suitable heater (not shown). The flow of electrons fromeach gun 27 and 29 is controlled in conventional manner by a grid, 35and 37 respectively.

Cathodes 31 and 33 are operated at different potentials with respect toscreen 13 by means described in greater detail hereinafter so thatelectrons emitted from the two guns are accelerated to differentenergies. The voltage between gun 29 and screen 13 is such that theelectrons emitted from this gun will energize only the red lightemitting phosphor particles 19. Gun 27, on the other hand, is at such apotential with respect to screen 13 that electrons emitted from that gunwill energize both the red and cyan light emitting particles 19 and 20respectively to cause substantially white light to be produced at screen13.

The respective intensities of the beams emitted from the guns 27 and 29are controlled by signals derived in accordance with the presentlystandard NTSC system of television broadcasting. It is to be understoodthat signals derived according to other transmission systems, e.g., PALor SECAM, may also be used to modulate the beams. A luminance signal(Y), obtained from a luminance amplifier YA, is applied to cathode 33directly and, through a D.C. blocking capacitor C1, to the cathode 31.Cathode 33 is maintained at D.C. ground potential. A conventional R-Ysignal is obtained from an R-Y amplifier RA and is applied to the grid37 of gun 29. Accordingly, as the electron beam from this gun is scannedover screen 13 by means described hereinafter, its intensity ismodulated in accordance with the long wavelength record or red componentof the composite video signal being received. Since the electron beamfrom gun 29 energizes only the red phosphor particles 19 as explainedpreviously, a corresponding red image is produced on screen 13 to beseen through face plate 15.

Similarly, a G-Y amplifier GA provides to grid 35 the conventional G-Ysignal. Thus the electron beam from gun 27 is modulated in accordancewith the green or short wavelength information in the composite videosignal. As it is scanned across the screen 13, the beam from gun 27energizes both kinds of phosphor particles 19 and 21 so that asubstantially white or achromatic image is produced. The red and whiteimages produced on screen 13 combine to form a composite image whichsubjectively appears to include a full range of hues, including thosewhich are not actually present in the colorimetric sense. This generaltwo-color system of presenting full color images is known in the art andprovides a pleasing appearance in which the hues appear more saturatedthan they really are.

The steps necessary for detecting the Y, R-Y and G-Y signals areconventional and, since they form no part of the present invention, arenot discussed further herein.

The electron beams emitted from guns 27 and 29 pass through theinfluence of a magnetic deflection yoke 39 which includes bothhorizontal and vertical deflection coils. The yoke is driven byconventional deflection circuits (not shown) to deflect the electronbeams for obtaining a scan or raster which sweeps screen 13. However, asthe electrons in the two beams travel at different velocities due totheir different accelerating voltages, the

electron beams are not equally deflected by the Same magnetic field. Thebeam which is accelerated by the greater voltage Will be less subject todeflection than the other beam or, in other words, will be stiffer. Forsmall differences in the accelerating voltages, the difference indeflection in relation to the total deflection is satisfactorilyrepresented by one-half the voltage difference in relation to the totalaccelerating voltage, i.e., AD/D is approximately equal to one-halfAE/E.

To offset or compensate for the difference in beam deflection, gun 27 isprovided with auxiliary electrostatic deflection plates 41 driven bybooster or auxiliary circuits (not shown) to obtain additionaldeflection. Only vertical deflection plates are shown, the horizontalplates being omitted from the drawing to avoid obstructing the view. Theadditional electrostatic deflection augments the magnetic deflection ofthe electron beam from gun 27 by yoke 39 thereby to achieve a totaldeflection which is equal to that experienced by the beam emitted fromgun 29 under the influence of the yoke 39 alone. Thus with acompensating signal of proper amplitude applied to the plates 41, thescanning patterns of the respective beams will be in register.

However, as may be seen from the deflection/accelerating voltagerelationships discussed above, the magnitude of the signal which must beapplied to plates 41 is highly dependent upon the voltage differentialbetween guns 27 and 29 in relation to the total accelerating voltagesbetween the guns and screen 13. If either the total accelerating voltageor the voltage differential between the guns varies independently, theneeded amount of deflection compensation will also vary and exactregistration will be lost. To vary the amplitude of the compensatingsignal would be cumbersome and expensive.

The present invention avoids this variation in the amount of deflectioncompensation needed by controlling the magnitude of the voltagedifferential in relation to total accelerating voltage in accordancewith the relationships presented above so that the required deflectioncompensation remains constant despite variations in the absolutemagnitude of the accelerating voltages. For small voltage changes, thenecessary relationships are maintained when the voltage differential isregulated as a fixed proportion of the total accelerating voltagebetween one gun and the screen. Thus a compensating signal of uniformamplitude applied to the plates 41 gives satisfactory registration eventhough there is some variation in the high voltage applied to screen 13.Accordingly, the need for regulation of the high voltage sup ly HV isavoided.

In FIGURE 1 an additional negative voltage is applied to cathode 31 withrespect to cathode 33, which additional negative voltage is regulatedwith respect to the high voltage positive potential applied to screen 13by the high voltage supply HV. The negative side of a low voltage supplyLV is connected to cathode 31 through a resistance R1 which permits thevoltage at cathode 31 to be shunt regulated. Resistance R1 may, forexample, be the inherent source impedance of supply LV. Cathode 31 isalso connected, through a current limiting resistor R2, to the collectorof a PNP transistor Q1. The collector is also connected to groundthrough a bleeder resistor R3.

A pair of resistors R4 and R5 constituting a voltage divider extendbetween the high voltage applied to screen 13 and ground. The junctionbetween resistors R4 and R5 is connected to the base terminal oftransistor Q1 to provide a positive reference voltage which is a fixedproportion of the screen voltage. The positive side of the low voltagesupply LV is connected to ground through a resistor R6 and a Zener diodeZ1, connected in parallel, thereby to provide a positive potentialsource with respect to ground at a junction 45. The parameters ofresistor R6 and diode Z1 are chosen such that this positive supplyvoltage is essentially equal to or of the same order of magnitude as thereference voltage applied to the base of transistor Q1 by resistors R4and R5. The emitter terminal of transistor Q1 is connected to thispositive potential source through a current limiting resistor R7.

The conductivity of the collector-emitter circuit of transistor Q1 is afunction of the relative values of the positive supply voltage atterminal 45 and the positive reference voltage applied at the base oftransistor Q1, the transistor Q1 being forward biased into conductionwhen the reference voltage falls below the positive source voltage.Accordingly, if the voltage applied to the screen 13 should decrease forany reason, the transistor Q1 will be biased into greater conduction.Conduction in transistor Q1 shunts negative current away from cathode 31so that the voltage differential between the two cathodes is reduced.The voltage differential between cathodes 31 and 33 is thus regulatedsubstantially in proportion to the total accelerating voltage appliedbetween cathode 33 and screen 13. As noted previously, such regulationessentially eliminates variations in the deflection correction needed sothat registration between the component images is maintained even thoughthere may be some change in image size.

In the embodiment illustrated in FIGURE 2, the cathode 31 is the onemaintained at DC. ground potential and a positive voltage is applied tothe cathode 33 to produce the desired difference between the energies ofthe electrons emitted from the respective electron beam guns 27 and 29.Accordingly, the capacitor C1 is placed in the lead between cathode 33and the Y amplifier YA so as to provide the necessary D.C. isolation.

In this embodiment auxiliary electrostatic deflection is not used butrather the electron beam guns 27 and 29 are provided with tubularmagnetic shunts, 43 and 44 respectively, which are of different lengths.The shunts 43 and 44 are operative to shield the respective electronbeam, over the length of the respective shunt, from the magnetic fieldscreated by the yoke 39. The shunt,43 is shorter than the shunt 44 sothat the electron beam from gun 27, which is emitted at a highervelocity than that from gun 29, will be subjected to magnetic deflectingforces for a longer portion of its path. Due to the longer exposure tothe deflection forces, the faster electrons emitted from gun 27experience a total deflection which is substantially equal to thatexperienced by the beam from gun 29 over a longer exposure path. Thusdeflection compensation is obtained so that the images pro- 'duced bythe two guns will be in register. This form of deflection compensationis discussed in greater detail in U.S. Patent 3,114,795. However, thisform of deflection compensation also is dependent upon the magnitude ofthe voltage differential between the two guns in relation to the totalaccelerating voltage.

To maintain the needed amount of compensation at a constant level, thevoltage differential between the cathodes 31 and 33 is requlated inresponse to the relative values of both the accelerating voltage and thedifferential voltage thereby to obtain an error-reducing feedback modeof operation. The positive side of a low voltage supply LV is connectedto cathode 33 through a resistance R11. Resistance R11 is also connectedas the load resistance of one (Q3) of a pair of NPN transistors Q3 andQ4 which are interconnected as a differential amplifier. The collectorterminal of transistor Q4 is provided with a load resistance R12 and theemitters of transistors Q3 and Q4 are connected to ground through acommonemitter resistor R13. Emitter resistor R13 effects thecross-coupling which provides the differentially responsive mode ofoperation of this circuit.

A reference voltage which is a fixed percentage of the voltage appliedto screen 13 by supply HV is applied to the base terminal of transistorQ4 by resistors R4 and R5, as in the previous embodiment. A pair ofresistors R14 and R15 connected between cathode 33 and groundconstitutes a second voltage divider which applies to the base terminalof transistor Q3 a feed-back voltage which is a fixed proportion of thevoltage differential existing between cathodes 31 and 33. Thedifferential amplifier circuit is responsive to the difference betweenthe reference voltage and the feed-back voltage to regulate thekinescope cathode voltage differential as a predetermined proportion ofthe screen voltage. If the screen voltage should fall for any reason,the forward bias applied to the base terminal of transistor Q4 isreduced and the voltage at the connected emitter terminals oftransistors Q3 and Q4 tends to fall. A reduction in the voltage at theemitter of transistor Q3 tends to increase its forward drive and thusincrease the current drawn from R11. The current drawn from R11 isshunted away from cathode 33 and thus the cathode differential voltageis lowered until the feed-back voltage, applied at the base oftransistor Q3, is again substantially equal to the reference voltage atthe base of transistor Q4. Accordingly, it is seen that the differentialvoltage is maintained at a fixed proportion of the screen voltagerelative to cathode 31 and thus the amount of deflection compensationneeded remains substantially constant.

FIGURE 3 schematically illustrates an embodiment in which the highvoltage divider resistors R4 and R5 are enclosed within a sealedkinescope envelope 49. As these resistors, particularly resistor R4,operate at very high voltages, they tend to attract and hold dustparticles if they are not protectedThus, if these resistors are in anexposed location, the accumulation of foreign material may createleakage paths which change the effective operation of the divider andinterfere with the proper operation of the voltage regulator accordingto the invention. By placing the divider within the sealed kinescopeenvelope this problem is avoided.

FIGURE 4 illustrates a further embodiment of a kinescope incorporating avoltage divider structure. In this construction a resistive film 51 isapplied to the inner surface of a kinescope envelope 53 in the generalform of a helical spiral which progresses from a screen 13 toward theneck portion 25 at which point it is grounded at a terminal 54. A tap 55allows a fixed proportion of the screen voltage to be taken off andemployed as the reference voltage in the regulator or control circuitsdescribed previously.

While regulator circuits employing transistors have been shown, it is tobe understood that vacuum tubes may be used as the circumstancesdictate. Also, while two guns operating simultaneously to provide twocomponent images have been shown, a single gun may be used by switchingbetween voltage levels to obtain a time sharing mode of operation. Theregulation of the voltage difference between the sequentially appliedvoltage levels as a fixed proportion of the absolute value of one ofthem yields the same deflection compensation advantages as in theillustrated embodiments. Similarly, if more than two guns are used,e.g., to obtain three or four color image presentations, the voltagedifferences between the guns are advantageously regulated as functionsof one of the total accelerating voltages. A continuous or incrementalvariation of accelerating voltages over a predetermined range can beused to vary hue in response to chrominance information. In such a casethe range traversed may be regulated as a function of the peakaccelerating voltage so as to maintain the deflection compensationneeded at a constant value.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:

1. A color display system comprising:

a viewing screen including phosphors which emit light of differentcolors when energized by electron beams of different energies;

electron beam gun means for emitting a beam of electrons toward saidscreen thereby to energize said phosphors;

voltage supply means for providing at least first and second electronbeam accelerating voltages, said second electron beam acceleratingvoltage being higher than said first electron beam accelerating voltage,to effect a beam of electrons of a first accelerating voltage and a beamof electrons of a second accelerating voltage for energizing saidphosphors to emit light of different colors;

deflection means for applying a first defletcion force to said beam ofelectrons of said first accelerating voltage and for applying a seconddeflection force to said beam of electrons of said second acceleratingvoltage to effect scanning of said screen by said beams of electrons,said deflecting means incorporating means for magnetically scanning saidelectron beam and incorporating means adjacent said electron beam gunmeans for applying an additional electrostatic deflection force to saidbeam of electrons of said second accelerating voltage, whereby saiddeflection force is greater for said beam of electrons of said secondand higher accelerating voltage;

a voltage divider for obtaining a reference voltage which is a fixedproportion of the accelerating voltages from said voltage supply means;and

a relatively low voltage supply which is responsive to said referencevoltage for providing a voltage differential between said first electronbeam accelerating voltage and said second electron beam acceleratingvoltage, which voltage differential is a predetermined function of saidreference voltage;

whereby registration is maintained between image components provided byelectrons accelerated by said first and second electron beamaccelerating voltages respectively despite variations in the absolutevalue of said accelerating voltages.

2. A color display system of caim 1, wherein said electron beam gunmeans includes two guns and wherein only said second gun is providedwith said second and higher electron beam accelerating voltage and onlythe electron beam from said second gun is additionally deflected by anelectrostatic deflection force as a part of said deflection means, andboth electron beams from both of said guns are subjected to saidmagnetic deflection means effecting magnetic scanning of said electronbeams.

3. A color display system comprising:

a viewing screen including phosphors which emit light of differentcolors when energized by electron beams of different energies;

a first electron beam gun;

a high voltage supply for providing an electron beam acceleratingvoltage at said screen with respect to said first gun;

a voltage divider for obtaining a reference voltage which is a fixedproportion of said accelerating voltage;

a second electron beam gun; and

a relatively low voltage supply which is responsive to said referencevoltage for providing a voltage differential between said first andsecond guns which voltage differential is a predetermined function ofsaid reference voltage whereby registration is maintained between theimage components provided by said guns despite variations in the voltageprovided by said high voltage supply.

4. A color display system as set forth in claim 3 in which said screenand said guns are incorporated into a kinescope having a sealed envelopeand in which said voltage divider is enclosed within said envelope.

5. The color display system of claim 3 wherein:

said low voltage supply is connected to afford an additive voltage ofpolarity opposite to the voltage at said screen, and

said voltage differential is effected by a non-inductive solid stateregulating circuit interconnected with said low voltage supply to lowersaid additive voltage in response to a lower voltage at said screen.

6. The color display system of claim 3 wherein:

said low voltage supply is connected to afford a partial voltage of thesame polarity as said voltage at said screen, and

said voltage differential is effected by a non-inductive solid statedifferential amplifier interconnected with said low voltage supply toadjust said partial voltage as a function of said voltage at saidscreen.

7. A color display system comprising:

a viewing screen including phosphors which emit light of differentcolors when energized by electron beams of different energies;

a first electron beam gun;

a high voltage supply for providing an electron beam acceleratingvoltage at said screen with respect to said first gun;

a voltage divider for obtaining a reference voltage which is a fixedproportion of said accelerating voltage;

a second electron beam gun;

a relatively low voltage supply for providing a voltage differentialbetween said first and second guns, said low voltage supply including anappreciable source impedance; and

a regulator circuit responsive to said reference voltage for shuntingcurrent from said low voltage supply away from said second gun therebyto control said differential voltage as a predetermined function of saidaccelerating voltage.

8. A color display system comprising:

a viewing screen including phosphors which emit light of differentcolors when energized by electron beams of different energies;

a first electron beam gun;

a high voltage supply for providing an electron beam acceleratingvoltage at said screen with respect to said first gun;

a voltage divider for obtaining a reference voltage which is a fixedproportion of said accelerating voltage;

a second electron beam gun;

relatively low voltage supply for providing a voltage differentialbetween said first and second guns;

a voltage divider for obtaining a feed-back voltage which is a fixedproportion of said voltage differential; and

a regulator circuit, responsive to the voltage difference between saidreference voltage and said feed-back voltage, for controlling currentflow from said low voltage supply to said second gun thereby to maintainsaid voltage differential equal to a fixed proportion of saidaccelerating voltage.

References Cited UNITED STATES PATENTS 7/1963 Rhodes 315-13 9/1966 Moleset al. 315-13 X US. Cl. X.R.

